It is widely known that ultraviolet (UV) light radiation, whether from a natural source such as the sun or an artificial source such as interior lighting, can accelerate both the physical and chemical deterioration or breakdown of polymeric resin materials. For example, it is known that UV light radiation causes the photodegradation of polyolefin resins such as polyethylene and polypropylene, the dehydrohalogenation of polyvinylhalide resins such as poly(vinylchloride) and the embrittlement of polyvinylaromatic resins such as polystyrene.
To protect these and other polymeric resin materials against the deleterious effects of UV light radiation, various commercial UV light absorbing additive agents have been developed. These commercial UV light absorbing additive agents generally provide protection to the polymeric resin material either by absorbing the UV light radiation directly or by harmlessly dissipating this particular light energy through intermolecular energy processes with the polymeric resin.
In the main, the most widely used commercial UV light absorbing additive agents are materials that are organic in nature and typically can be grouped into five basic categories. These groups are (1) hydroxybenzophenones, (2) hydroxyphenylbenzotriazoles, (3) salicylates, (4) arylsubstituted acrylates and (5) aminobenzoates. Other miscellaneous UV light absorbers that have been used include various nickel chelates, nickel complexes and nickel salts of various aromatic compounds.
One inorganic material that is known to be useful as an additive agent to provide UV light stability to polymeric resin materials is the pigmentary metal oxide, titanium dioxide. In U.S. Pat. No. 4,619,957 it is disclosed, for example, that pigmentary titanium dioxide can be added to rigid poly(vinylchloride) resins not only to provide for the proper pigmentation of formulations based on these particular resins but also to prevent significant color variations from occurring in products fabricated therefrom upon subsequent exposure to UV light radiation. However, according to this patent, a problem associated with the use of titanium dioxide in such formulations is that, due to its high opacity and tinting strength, products fabricated from such formulations can be produced only in white or pastel colors. Although darker shades or colors can be obtained either by adding larger amounts of colorant or by reducing the concentration of the pigment, such approaches only add to the cost of such formulations or reduce the UV light stability of finished products prepared therefrom.
While it is clear from the above disclosures that many different UV light absorbing additive agents have been employed to provide UV light stability to various polymeric resin materials, a need still exists for UV light absorbing agents that are less costly than the above disclosed organic agents and which are capable of overcoming the drawbacks associated with such inorganic agents as titanium dioxide. The UV light absorbing pigmentary compositions of matter of the present invention fulfill this need.